The present invention relates to hydraulic pumps, and in particular to in-line axial piston pumps.
Conventional in-line axial piston pumps have a plurality of pistons in multiple bores of a single piece cylinder barrel. The cylinder barrel is keyed to the drive shaft and is rotated by a prime mover, such as an electric motor. The cylinder barrel and the pistons are parallel to the drive shaft. As the cylinder barrel rotates within the pump housing, the pistons follow an inclined surface of a swash plate thereby reciprocating in their bores. The reciprocal motion of the pistons produces a pumping action.
The swash plate typically is a steel ring that is held at an acute angle with respect to the axis of the drive shaft. During one-half of the shaft rotation, each piston is pulled from its bore which draws fluid into that bore. Upon reaching the maximum extended position, the piston starts traveling along a portion of the inclined swash plate which pushes the piston into the bore thereby forcing the fluid to flow out of the pump.
The displacement of a given pump is determined by the number of pistons, each piston's diameter and the length of the stroke. The steeper the angle of the swash plate, the longer the piston's stroke. In a variable displacement pump, the angle of the swash plate can be changed dynamically to alter the stroke and thus the pump displacement.
Pumps of this design are well known and are commonly used in aircraft hydraulic systems. In aircraft applications, the size and weight of the pump are critical. Therefore, any improvement which reduces these factors will have benefit in aircraft usage.